Some conventional chargers, e.g., switch mode battery chargers, control a charging current by monitoring a current through a current sensor. The charger can include an input current amplifier that is coupled to the current sensor and for monitoring the charging current. Such sensing method may be accurate when the voltage drop on the sense element is relatively big, e.g., greater than 50 mV. However, problems may occur when the charger controls a relatively small charging current, e.g., during wake-up charging, trickle charging, or end of charging.
One of the issues is caused by an offset of the input current amplifier, which can be in the range of 2 mV-3 mV. For example, when the charging current is relatively small, the sensing error may reach up to 100%.